Abstract

At the VNIItekhmash, optimum processing techniques have been developed for the end face treatment of individually cast piston rings, 230-300 mm in diameter, using universal machines in conditions of mass production. The new technology eliminates the pretreatment of the end faces of piston rings inlathes, making it possible to reduce the thermal straightening time to a considerable extent, while ensuring the required finish.The quality of the end face finish of piston rings should be top grade. The warping allowance should not exceed 0.05 ram. The surface finish should be V7-V8. The variation in thickness along the height should be within fitting allowance limits Sh.The investigations were carried out in industrial conditions at the Vienybe Works (Lithuanian SSR). A batch of 125 cast piston rings, 230 and 270 mm in diameter, was selected for the test. It was found that the warping of the 230 mm diameter rings was 0.2-0.8 mm, and that of the 270 mm diameter rings was 0.1-0.35 mm.Since the technology of casting blanks of piston rings used at the Vienybe Works includes minimum machining allowances, the end faces were premachined in a 3B756 surface grinder equipped with a round magnetic table.Measurements showed that rough grinding reduced the warping of rings approximately by 50%.Warping can be reduced to the allowance limits by thermal straightening in a special device of simple construction (see Fig. 1), using the following method.The rings are cleaned and washed, assembled in the device, tightened by means of the wedge and pressed, and then charged into a furnace heated to a temperature of 550-570~The rings are held at this temperature for 2.5-3 h, and then removed from the furnace and air cooled together with the device.To determine the effect of the heating temperature during thermal straightening on the degree of warping and hardness of the rings, the investigation was carried out at temperatures 550 •176 and 570 •176It was found that in both cases the results obtained were stable both with respect to the degree of warping and the strength which hardly varied.